Toxocara (the cause of visceral larva migrans in humans) and allergy have in common both elevated immunoglobulin E (IgE) levels and eosinophilia. In the present study, we investigated: 1) associations between Toxocara seropositivity and allergic manifestations; 2) risk factors for Toxocara infection; and 3) differences in Toxocara seroprevalence, allergic manifestations and the associations between these two, in children from urban and rural environments.Blood samples from 1,379 Dutch urban and rural elementary schoolchildren, were examined for Toxocara antibodies, eosinophil numbers, total IgE concentrations, and the occurrence of inhaled allergen-specific IgE. Questionnaires investigating respiratory health and putative risk factors for infection were completed.It was found that 8% of the children had Toxocara antibodies, occurring significantly less often in females than in males. The means of total serum IgE levels and blood eosinophils were significantly higher in the Toxocara-seropositive than in the seronegative group. Allergic asthma/recurrent bronchitis was found in 7% of the children, allergic reaction on animal contact in 4%, and IgE to at least one inhaled allergen in 16%. These variables were associated with Toxocara seroprevalence. Inhaled allergen-specific IgE and asthma/recurrent bronchitis occurred significantly less often in rural than in urban areas, and significantly less often among girls than among boys. Furthermore, occurrence of allergen-specific IgE increased significantly with age. No association existed between Toxocara seroprevalence and assumed risks, i.e. contact with pet animals and public playgrounds.In conclusion, our results indicate that allergic manifestations occur more often in Toxocara-seropositive children. A relationship with an already existing allergic condition is plausible. Eur Respir J 1997; 10: 1467-1475 Recent investigations suggest an increasing prevalence of childhood asthma [1,2]. Children at risk are those with an atopic constitution [3,4]. The age at which allergy becomes manifest depends mainly on the degree of exposure to inhaled allergens, the most obvious being that to house dust mite (Dermatophagoides pteronyssinus) allergen [5]. Frequent exposure to allergens may accelerate expression of allergic symptoms at a young age [6]. Various products of biological origin, such as antigens derived from parasitic worms, have polyclonal B ε -cell-activating properties, and can, thereby, induce high serum total immunoglobulin E (IgE) concentrations [7,8].Toxocara spp., intestinal parasites of dogs and cats, may spend part of their life cycle in noncompatible hosts, including humans. Toxocara is endemic in the Netherlands. About 8% of the children have antibodies to this roundworm [9]. Eggs are passed on the soil with dog/cat faeces; the infection, therefore, is soil transmitted. Larvae, hatched in the intestine from ingested eggs, migrate to the body tissues, such as liver and lungs. In noncompatible hosts, the larvae do not develop, and may survive as such...

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